1. Field of the Invention
The present invention relates to an electronic musical instrument having an automatic rhythm performance device, and more particularly to an electronic musical instrument capable of changing the number of rhythm tones played in response to operation of an expression pedal (hereinafter referred to as an "EXP pedal") for sound volume adjustment.
2. Description of the Prior Art
Prior electronic musical instruments such as electronic organs having an automatic rhythm performance device are capable of increasing the volume of musical tones produced by a keyboard in response to operation of an EXP pedal, of enriching a harmony in response to operation of a tone lever, and of increasing a sound pitch thereby strengthening the effect of performance. However, rhythm tones are fixed throughout the performance of a music piece once a particular rhythm is selected. Therefore, rhythm tones based on one selected rhythm source will be simply repeated from the beginning to the end of a music piece played.
Some electronic organs have a rhythm variation switch for changing rhythm patterns. However, the rhythm variation switch fails to change rhythm sources and thus is incapable of sufficiently enhancing the effect of performance of rhythm tones. As a player of an electronic organ gets involved more and more deeply in the performance of a music piece, the player is normally inclined to devote all his efforts to the playing of the keyboard. The rhythm variation switch is usually mounted on a panel or a key block and hence cannot easily be operated upon.
To solve the difficulty in actuating the rhythm variation switch during performance, Japanese Patent Preliminary Publication No. 58-18694 discloses an arrangment for automatically producing a bass drum sound when the EXP pedal is depressed beyond a certain stroke. With this arrangement, a bass drum sound and various other rhythm tones are automatically performed according to respective rhythm patterns read out of a pattern memory in response to a count from a tempo counter. When the EXP pedal is depressed beyond a certain depth, only the bass drum sound is automatically replaced with a bass drum sound successively produced in minimum rhythm units constituting its rhythm pattern in response to a bass drum sound signal from a percussive-instrument-sound adding circuit. However, since the prior rhythm tone is suddenly replaced with a successive bass drum sound when the volume of the musical tone played goes higher than a certain level, a smooth increase in the volume of the musical tone played by the keyboard is not fully matched by a buildup in automatic rhythm performance.